Even before Hurricane Katrina assaulted New Orleans and submerged four-fifths of the city, Mayor Ray Nagin had become a crooked politician.

When Nagin launched his underdog campaign in 2001, voters fell in love with the idea that a big shot executive would take a pay cut to straighten things out on the second floor at City Hall.

That narrative would have been heartening had it been true.

But the truth was that in one of the poorest cities in the United States, Nagin found that he couldn’t make ends meet on $150,000 a year.

He began to sponge off his best friend, businessman David White, taking $3,000 a month. And when that wasn’t enough, he asked for $7,500. He changed the way the city selected technology vendors, then took a Hawaiian vacation financed by the businessman who benefitted.

Katrina changed New Orleans in so many ways, but it didn’t change Nagin.

The politics of the city became a giant reality show for the rest of America, and Nagin was the star, preening before TV cameras during a campaign so chaotic that they had to postpone election day.

A city struggling to overcome the costliest disaster in U.S. history could have used its own Rudy Giuliani, but in Nagin it got a Boss Tweed.

After the votes were counted, he went back to being a crook, with more gusto than ever, and, thanks to the economic boom created by the recovery, more chances to make a buck.

Representatives of businesses and charitable groups looking for ways to help the struggling city complained they could not get the attention of the mayor.

But Nagin was tirelessly attentive to the needs of his family’s granite countertop business, Stone Age. When Home Depot sought to build an outlet at Earhart and South Claiborne to take advantage of the expected building boom, the mayor relieved the retail giant of obligations to hire and train residents of the nearby neighborhood.

In turn, he shook down Home Depot to steer business to Stone Age and griped when his firm didn’t get as much work as he expected, signing his message “Mayor Ray Nagin.”

In addition to the truckloads of granite he received, Nagin collected about $250,000 in cash, enjoyed free lawn care and jetted to Las Vegas, Jamaica and New York on other people’s dimes.

Jurors hardly broke a sweat in February, convicting him on 20 of 21 counts.

Wednesday, his sentence will be decided by U.S. District Judge Ginger Berrigan. Berrigan stands out at Poydras and Camp as a liberal judge in a conservative courthouse, and she has been known to find sympathies for criminals that her colleagues might not see.

But federal sentencing has its own protocols, with bureaucrats making a recommendation based on factors like the seriousness of the crime and the history of the defendant. In Nagin’s case, the recommendation could amount to more than 20 years.

The judge does not have to follow the guidelines, but a defendant as cavalier and remorseless as Nagin hardly deserves a break.